An estimated 10 million patients undergo an operative procedure annually in the United States. Despite overall improvements in outcomes, over 120,000 people die following surgery each year in the US. Many more will suffer from adverse events. Nascent research suggests that a significant proportion of the variation in outcomes occurs at the level of the operative surgeons. Yet, recent changes in the nature of surgical care, increased scrutiny of surgical outcomes, and duty-hour reform have dramatically changed the surgical training process. Resultant concerns regarding the quality of the modern new surgeons are substantiated by the recent sharp increase in the oral board failure rate. To date, no one has been able to examine the quality of the modern new surgeons because they have only recently entered the workforce. Using the introduction of the duty-hour reform in 2003 as a landmark for the larger set of systematic changes, we aim to understand the effects of environmental changes on the quality of care provided by new surgeons and the public health implications of changes in the surgical field on the emerging surgical workforce. In this proposal, using a customized Medicare claims dataset including all new surgeons across 50 states, we will use a novel two-step matching process developed specifically for this study and a difference-in-difference (D-in-D) approach to examine the effects of training in the modern era on the new surgeon product. New surgeons will be classified as modern or traditional by the year in which they entered residency. Surgeon pairs will be constructed for the modern (AY 2009-2013), transitional and traditional (AY1999-2003) training eras. The first step of the two- step match pairs new and experienced surgeons by the surgical procedures they performed at the same hospital in the same time period. Step two matches individual patients inside each matched surgeon pair. Using this two-step matching approach, we can control for procedure, technical and patient characteristics such that the patients treated by new and experienced surgeons within hospitals will be virtually identical. The D-in-D approach using experienced surgeons as controls minimizes confounding associated with changes in the delivery of healthcare over time. Post-match regression will be used to control for residual confounders like fellowship status. Subset analysis will permit focused examination of specific clinical cohorts to provide transparently meaningful results. Moreover, we will derive time to proficiency curves across multiple specialties and within specific clinical cohorts. Aim 1 will examine clinical outcomes and Aim 2, economic outcomes. After completing the project, we will be able to 1) inform the ACGME and ABMS on gaps in new surgeon performance for subsequent education reform, 2) use the methodology developed for this proposal to monitor any future reform and 3) advise CMS (and other payors) and surgeons on strategies for focused professional development programs (e.g., surgical coaching or phased privileging or credentialing) to improve the quality of care delivered to surgical patients today and safeguard the care of surgical patients in the future.